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Donor interaction studies in phosphites, phosphates and oxyphosphoranes: Models for activated states of phosphoryl transfer enzymes
Abstract
Higher coordination by donor atom interaction in phosphites and phosphates has until recently been a relatively unstudied aspect of phosphorus chemistry. The complexes involved are postulated as models for enzyme-phosphate substrates in phosphoryl transfer systems. Donor atoms employed in these compounds include sulfur and oxygen, which are typically present in enzyme residues at active sites of phosphoryl transfer enzymes. The degree of donor atom coordination is measured by the distance between the central phosphorus atom and the donor atom. This is reinforced by a measurement of the degree of distortion of the tetrahedron toward trigonal bipyramidal structures (in the case of phosphates) and pseudo-trigonal bipyramidal structures (in the case of phosphites). Hypercoordination by donor atom interaction in pentaoxyphosphoranes is well documented. Again, donor atoms used have included sulfur and oxygen. The degree to which the donor atom interacts with the phosphorus is obtained by measuring the distance between the two atoms and by the extent of distortion of the trigonal bipyramid toward an octahedral structure. These measurements are gathered from the molecular structures which are determined by X-ray crystallography. Other methods which are used for structure elucidation include $\sp1$H and $\sp{31}$P NMR spectroscopy. Six phosphites are synthesized, five of which contain the highly electronegative pentafluorophenoxy group. The effect of this group and of the varying aryl substituents on the coordination abilities of sulfur and sulfonyl oxygen atoms is discussed. Also included for comparison are two phosphites which contain no donor atom coordination. Three phosphates are synthesized, one of which contains a pentafluorophenoxy group. The effect on donor coordination by placing a phosphoryl oxygen atom in place of a lone pair in the analogous phosphite structure is discussed. Twelve phosphoranes are synthesized, eight of which exhibit donor atom coordination and are octahedral while four shown no donor interaction and are trigonal bipyramidal. Of the hexacoordinate phosphoranes, five were prepared via oxidative addition of a quinone and two via displacement reactions of monocyclic pentaoxyphosphoranes. Penta- and hexacoordinate phosphoranes are considered as models for activated states for phosphoryl transfer enzymes. The effect on reaction rate of tighter binding in the six-coordinate enzymatic transition state relative to both the five-coordinate transition state and the enzyme-phosphate substrate is discussed. The reactivities of a series of known oxyphosphoranes with respect to nucleophilic displacement by catechols is also described. The effect of varying substituents and extent of donor coordination on reaction rates are discussed.
Subject Area
Chemistry|Materials science
Recommended Citation
Sood, Paul, "Donor interaction studies in phosphites, phosphates and oxyphosphoranes: Models for activated states of phosphoryl transfer enzymes" (1998). Doctoral Dissertations Available from Proquest. AAI9909223.
https://scholarworks.umass.edu/dissertations/AAI9909223